A service tag is an 84-bit description of a given map.
The lower 53 bits are the map seed.
The upper 31 bits describe the parameters given to the map generator.
They are:
BLLC.CCNA.MPPR.RRII.WWYY.YYYY.HHED.D##S [The rest is for the 53-bit seed]
B: Minimize large continents being split at international date line
L: Land percent
C: Climate
N: New world (0: Start anywhere reasonable; 1: new world or same landmass)
A: Allow Pangeas
M: Eliminate coastal mountains and reduce other mountains
P: Patience
R: Map ratio
I: Island factor
W: Map wrap
Y: Vertical map size
H: Player handicap (bonus resources)
E: Everyone on same landmass (0: No 1: Yes [New world also has to be set])
D: Map Resource distribution
#: 2-bit "parity" of all other digits in service tag; error check
S: Map seed